Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financial assets
Available-for-sale marketable securities	$ 81,219	$ 91,640
Corporate Bonds [Member]
Financial assets
Available-for-sale marketable securities	14,579	14,188
Recurring [Member]
Financial assets
Total financial assets	86,233	107,441
Recurring [Member] \| Corporate Bonds [Member]
Financial assets
Available-for-sale marketable securities	14,579	14,188
Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets
Total financial assets	5,014	15,801
Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Financial assets
Total financial assets	81,219	91,640
Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member]
Financial assets
Available-for-sale marketable securities	14,579	14,188
Recurring [Member] \| Money Market Mutual Funds [Member]
Financial assets
Cash and cash equivalents	3,545	15,101
Available-for-sale marketable securities	31,288	41,986
Recurring [Member] \| Money Market Mutual Funds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets
Cash and cash equivalents	3,545	15,101
Recurring [Member] \| Money Market Mutual Funds [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Financial assets
Available-for-sale marketable securities	31,288	41,986
Recurring [Member] \| Commercial Paper [Member]
Financial assets
Available-for-sale marketable securities	21,695	19,442
Recurring [Member] \| Commercial Paper [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Financial assets
Available-for-sale marketable securities	21,695	19,442
Recurring [Member] \| Other U.S. Government Agency Obligations [Member]
Financial assets
Available-for-sale marketable securities	11,152	13,496
Recurring [Member] \| Other U.S. Government Agency Obligations [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Financial assets
Available-for-sale marketable securities	11,152	13,496
Recurring [Member] \| U.S. Treasury Securities [Member]
Financial assets
Available-for-sale marketable securities	2,505	2,528
Recurring [Member] \| U.S. Treasury Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Financial assets
Available-for-sale marketable securities	2,505	2,528
Recurring [Member] \| Bank Certificate of Deposit [Member]
Financial assets
Restricted cash		700
Recurring [Member] \| Bank Certificate of Deposit [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets
Restricted cash		$ 700
Recurring [Member] \| Commercial Money Market Account [Member]
Financial assets
Restricted cash	1,469
Recurring [Member] \| Commercial Money Market Account [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial assets
Restricted cash	$ 1,469

Cash and equivalents whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements.

No definition available.

+ Details

Name:	cara_RestrictedCashFairValueDisclosure
Namespace Prefix:	cara_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=cara_OtherUsGovernmentAgencyObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=cara_CommercialMoneyMarketAccountMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: